1. Field of the Invention
This invention relates to glycerol soldering fluxes and more particularly to flux bath compositions containing chelating salts dissolved in a glycerol solution.
2. Description of the Prior Art
In soldering electrical connections or surface soldering printed circuits, it is usually necessary to employ fluxes to wet, remove tarnish and activate the metallic surfaces being soldered. In addition, the flux must protect the activated surfaces against any passive film formation during alloying of the solder to metal circuits or surfaces being joined. To be effective, the flux bath has to be useful and operative at the soldering temperature employed. Furthermore, both the flux and flux residues have to be easily removable and/or non-corrosive to the metal contacts being soldered.
Prior art fluxes used in immersion bath soldering had the disadvantage of a narrow useful temperature range, a limited temperature life in high preheat exposure, a residue that was difficult to remove because of innate polymerization and retained flux activators becoming ionized by water leaching to promote local corrosion or low insulation resistance hazards. In addition, those prior art flux residues that required organic solvent cleaning to remove them, exposed organic encapsulating and laminate materials to a potential solvent degradation action involving swelling or partial dissolution thereof. Further, sometimes toxic vapors are emitted from the heated glycerol fluxes and contribute to the pollution level of the atmosphere.